Plastometer



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M. MooNEY iLAsTdM'ETER Filed Aug. 11, 1952 April 14, 1936.

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M. MOONEY PLASTOMETER Filed Aug. 1.1, 1932 4 sheets-sheet l 2 INVENTOR iApril 14, 1936. v M. MOONEY 2,037,529

PLASTOMETER Filed Aug. 11, Y1932 4 sheets-snaai s ZH @la V//r fam/ffATTORNEY kuni@ .5

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PLAsToMETE-R Filed Aug. 11, 1952 AApril 14, 1936.

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Patented Apr. 14,l

UNITED Melvin Moo 'Ihis invention relates 'PATENT 4oFF-ICF.

PLASTOMETEB.

by mesne of New Jersey ney, East Rutherford, N. J., assignor,assignments, to United States Rnbber Company, New York, N. Y.,

a. corporation Application August l1, 1932, Serial No. 628,347

11 Claims. v (Cl. 265-41) to plastometers and.

more particularly to an improved type of instrument for measuring theviscosity and the elastic recovery of rubber and plastic materialsgenerally.

The term "plastometer as applied to the present invention refers to aninstrument for making certain quantitative physical tests on plasticmaterials, which tests are known to be related in a general way with theplasticity of the material, or the ease with which the material can beshaped or formed in manufacturing processes.

vthere is no generally accepted quantitative deflnition of the property,plasticity, it is preferred to speak of measuring with the plastometer,not the plasticity, but those other properties whichhave been givenprecise and generallyaccepted definitions, such. as viscosity andelastic recovery. Experienced rubber technologists can make a roughestimate of the plasticity of a piece of rubber or compounded stock bypinching or stretching it, observing its calendar, or by other simpletests. A rough relabehavior on a mill or tive measure oi' plasticity isobtained by measuring the thickness of a sample which has been cut froma mill operating under standard conditions, and allowed to shrink orrecover.

For making accurate measurements of the plasticity,

various instruments have been/used,

4all of them falling under the two ciassiilcations of (1) the extrusionplastometer, rst used by B. Marzetti (Giorn. Chem. page 342; Rubber Ind.Appl., July 1923,

Age, vol. 6, page 139, 1925);

and (2) the'compression plastometer, rst used by Ira Williams (Ind. Eng.Chem., vol. l16, page In the extrusion plastometer, the rubberl ispacked into a cylindrical chamber, brought toa ilxed temperature,chamber through a pressed air .or by a piston. through the measured.

and then forced out of the small orice, either by com- The rate ofextrusion oriflce under a xed pressure is In the compressionplastometer, a pellet of rub.

ber of standard size and ilxed temperature, and fixed weight.v Thepellet is then interval or intervals. also be determined with measuringthe thickness of shapeA is 'heated to a.l

then compressed under a thickness of the compressed 'measured-after anychosen time The elastic recovery may this instrument by the pellet at achosen Since tion is negligible in comparison with the plastic 10 orpermanent deformation, and (c) that the vertical ilow is negligible incomparison with the radial ow. A more general treatment of this Aproblemwas recently published by J. R. Scott (Trans. I. R.. I., vol. 7. Dp.169-186, 1931). In 15 Scotts analysis the viscosity is assumed to varywith the shearing force according vto certain laws, and to beindependent of the extent vof deformation. Assumptions (b) and (c) madeby Healy are retained. It isnecessary to make these sim- 2 plifyingassumptions in order to carry through the mathematical analysis of theproblem, but since the assumptions are only approximations to thet/ruth, the viscosity calculated from the resulting formulae is roughlycorrect jin order of 25 magnitude but not exact.

One disadvantage of the extrusion and compression plastometers is thatthe measurements are not reliable unless the -s'amplescan be obtainedfree from all bubbles and air pockets. Another disadvantage of thesetypes of plastometer is that measurements obtained with them arenecessarily aiected by the thixotropy of raw rubber, that is, itstendency to hardenagain after being milled. This thixotropic eiect,whichis quite marked in rubber, is distinct from the obvious hardeningwhich accompanies cooling, as

it maybe observed in' samples which are all y measured at the sametemperature but at diierent time intervalsafter milling. In the extru-40 sion plastometer, for example, the rubber is given a single ilnitedeformation angl for all practical purposes this is true of thecompression plastometer, since after the rubber has been deformed by acertain amount, further travel of the weight becomes too-slow forsatisfactory measurements. Consequentlmas above stated, measurementsobtained `with these plastometers are affected by the thixotropy of theplastic Vmaterial to be testtrusion and compression types of plastometeris the time required to make a determination. Most of this time is takenup in bringing the sample to the temperature of the test, the preheatingperiod varying from 12 to 60 minutes, depending upon the size and shapeof the sample. Forming the sample is an additional operation, which alsorequires considerable time. e

An object of the present invention is to provide an instrument formeasuring the viscosity of rubber and plastic materials generally, inwhich the material is subjected to continuous shearing action. It isalso an object of the invention to provide a plastometer in which theseparate operation of preparing the sample is practically eliminated andin which the time necessary for a complete determination of theviscosity is reduced to a minimum.

Itis a further object of the invention to provide a plastometer in whichall air enclosed with or in the sample to be tested is worked out by theshearing action on the sample during the test.

It is also an object of this invention toprovide a plastometer in whichthe plastic material may be sheared continuously for any desired timebefore measurements are made, and thereby be brought to a soft plasticcondition, such for example, as rubber will attain on a. warm-up mill,such operation reducing to a negligible amount the effect of thethixotropy of the plastic material on the measurements taken.

It is also an object of the invention to provide a plastometer whereinthe plastic material is subjected to simple shear as contrasted withdouble or triple complex shears. A general treatment of shearing, andother strains appears in A. E. H. Love, The Mathematical Theory oi.AElasticity, third edition, Cambridge Press, chapter 1, articles 2, 3,14, 16.

It isa further object of the invention to provide an instrument whereinseveral pieces of the plastic material to be tested taken from diierentplaces in a batch may be combined as a single composite sample, therebyyielding the average plasticity of the batch-with a single measurement.I' A It is a further object of the invention to provide a plastometerwhich kwill measure the absolute viscosity or fluidity of a plasticmaterial, and also its elastic recovery. i

Other objects and advantages of the invention4 will more fully appearfrom`the following detailed description taken in connection with theaccompanying drawings, in which: A'

Figure 1 illustrates a vertical section 'on the line I-I oit'v Fig. 2,of a laboratorytype research plastometer; v a

Fig.'2 represents a horizontal section on the line 2 2 of Fig. 1; Y

Fig. 3 shows a detailed view of parts oi.' the construction shown inFig. 1 in operative position;

Fig. 4 shows an enlarged view of the rotatable corrugated cylinder ofthe instrument shown in Figs. land 2;

Fig. 5 represents a section on the line 5-5 of Fig. 1:

Fig. 6 illustrates a vertical section on the line 6 6 of Fig. 8, of aplant type of experimental and control plastometer; Fig. 7 represents avertical section onthe line 1-1 'of Fig. 6;

Fig. 8 shows a plan view of the base of the-instrument taken n the line8 8 of Fig. 7;

ed. Another practical disadvantage of the ex` Fig. 9 is a detail view ofthe stop mechanism shown in Fig. 1; and

Fig. 10 is a detail view of a latch mechanism shown in Fig. 1.

The invention broadly consists of aprocess and apparatus vformeasuringthe viscosity and elastic recovery of plastic or semi-solid materialswherein the material is subjected to a continuous shearing action. Twotypes of instruments are disy closed in the instant application, namely,a socalled laboratory type research plastometer, shown in Figs. 1 to 5,and a so-called plant type experimental and control plastometer shown inFigs. 6 to 8, but modifications of the apparatus shown may be readilymade without departing from the present invention. The measurement ofthe Viscosity in these two typesof instruments is obtained while thesample of material to be tested is subjected to a continuous shearingaction, and the sample is maintained under a continuous confiningpressure while being so sheared in order to produce a true shearingaction and prevent slippage of the material. Moreover, the shearingaction is further characterized in that it is effected by simple shear,as'contrasted with double or triple complex shears.

The average viscosity of a plastic material subjcted to shearing actionin the plastometer is proportional to the total shearing force dividedby the average rate of shear, or

Average coefficient of vscosity= total shearing force average rate ofshear It may readily be seen that if the ratio of the shearing forcetothe rate of shear can be determined, we have a measurement of theviscosity of the material in arbitrary units, that is, the relativeviscosity, andif the constant of the instrument can be determined, thenwe may obtain the absolute viscosity of the material tested. Indetermining the ratio of the shearing force to the rate of shear, it isevident that if the material is subjected to a iixed shearing force andthe rate of shear is measured, or if the material is subjected to afixed rate of shear and the shearing force, or the resistance oftheplastic material to the shearing action, is measured, then we may obtainthe ratio of the shearing force to the rate of shear; and if theconstant of the instrument is known, we may also obtain the absoluteviscosity of the material.

In the laboratory research type plastometer, shown in Figs. 1 to 5, theplastic material is subjected to a ilxed shearing vforce which isresolved in the` instrument into a xed and uniform shearing force perunit'area,r and the rate of shear of the material under this iixedshearing force is measured. The rratio of the xed shearing force to themeasured rate of'shear will thus give a measure oi' the relativeviscosity of the material. Furthermore, the constant of the, instrumentcan be derived theoretically, and the absolute viscosity of the materialmaytherefore be determined.l

In the plant type oi' experimental and control constant X plastometer,shown in Figs. 6 to 8, the plastic be calculated from the geometricaland other characteristics ofthe instrument, as is ldone with thelaboratory type research plastometer, but the geometry is less simple inthis case and the calculation is less exact. It is simpler, if it isdesired to cbtain absolute measurements of viscositv, to calibrate theinstrument with plastic materials standardized in the laboratory typeresearch plastometer. However, although the applied rate of shear inthe' factory type plastometer is fixed and constant, the actual shearingrate is not uni- Referring to Figures 1 to 5, wherein like refer- -encecharacters designate the same parts throughout the several views, Irepresents a table to which the base plate |I of the instrument isbolted and from which it is separated by suitable spacer means as shown.Attached to the base plate II are standards I2 and I3 to the upper endsof which is attached the top plate I4 of the instrument. In bearingblocks I5 and I6 in the base and top plates I I and I4 respectively, ismounted a rotatable hollow shaft I1 to which is keyed at some distancebelow the top plate I4 a cylindrical rotor I8 having verticalcorrugations I9 .in the center portion thereof and whose end portionsare reduced and smooth, as shown in detail in Figures 3 and 4.

Co-axial with and spaced radially from rotor I8, is a non-rotatingcylindrical surface or stator 2| with vertical corrugations 22 similarto the corrugations I9 on the rotor I8, and forming therewith an annularchamber 23 with vertically corrugated walls and into which the plasticmaterial to be` tested is placed. The .cylindrical surface 2| is formedin the surfaces of vtwo cooperating swinging blocks 24 and 25, hinged at26 about a sleeve 21 on the standard I2. The blocks 24 and 25 may beswung from the position shown in section and clamped together and aroundthe standard I3 by means of bolt 28 and nut 29 hinged on 'the block 24and cooperating `with block 25, as shown in Fig. 2i vThe corrugations inthe cylindrical surface 2| in the blocks 24 and 25 are of the samelength as the corrugations-I9 in the cylinder I8, the upper and lower',margins 30 and 3| of the cylindrical surface 2| being recessed andsmooth as shown in detail in Fig. 3. Collars 32 are attached to thestandards I2 and I3 above and below the blocks 24v and 25.'

On `the top and bottom surfaces of the blocks 24 and 25 are beveledguide plates 33 and 34 cooperating with the smooth upper and lowermargins 3|] and 3| ofthe cylindrical surface 2|. In Figs. 1 and 3 areshown the` top and lbottturi beveled guide plates-33 and 3 4 of theblock25. Corresponding beveled guide plates arealso attached to the top andbottom of block 24. The

top beveled guide plates 33 on the blocks 24 and 25 are shown in detailin Fig. 5. The plates 33 are free to rotate on the screws 35 and areguided into place by the screws 36. The plates -33 may be clamped `intooperating position as shown in Fig. 5 by tightening the screws 36orbyany other suitable clamping means. .The bottom beveled guide plates34 on the blocks 24 and 25 are constructed similar to the top guideplates 33.

Surrounding the reduced upper and lower portions of the cylinder I8 arebeveled collars 31 and 38 which are free to rotate on the shaft I1 andare held in place by sleeves 39 and 40 secured by set screws to theshaft I1 and rotating therewith. The smooth upper and lower margins 30and 3| of the cylindrical surface 2| form with the freely rotatablecollars 31 and 38 surrounding the reduced end portions 20 of thecylinder I 8, annular reservoirs 4| and 42 for plastic material held inreserve to maintain pressure in the annular chamber 23. Coniiningpressure is maintained 4in the reservoirs 4| and 42 by means of pressurerings 43 and 44 faced with vulcanized rubber pads 45 and 46. The upperpressure ring (shown out of engagement with the reservoir 4I in Fig. 1,and acting on the material in the reservoir to maintain pressure on thesame in Fig. 3)

is guided in its vertical movement by a guide 41 surrounding the shaftI1 and attached to the top platev I4. A weight 48 on lever arm 49 whichis pivoted at 50 in a pivot block 5I, attached to the standard I3 abovethe upper collar 32 on the standard I3, and which is connected to thepressure ring 43 at 52, maintains a constant pressure on the rubber ring45 in contact with the material in the reservoir 4 I. The lower pressurering 44 is adjustably mounted in plate 53 which is guided in itsvertical movement by the standards I2 and I3. A weight 54 is hung onlever arm 55 which is pivoted at 56 on the intermediate plate 51 of theinstrument. The other end of the lever arm engagesthe pressure ring 44and maintains a constant pressure on the rubber ring 46 in contact withthe material in the reservoir 42. I The intermediate plate 51 isattached to the standards I2 and I 3 and contains a bearing block 58 inwhich the shaft I1 is rotatable.

Depending from the intermediate plate 51 is a sleeve 59 in which theshaft I1 is rotatable. A

raceway or bearing 4block '60 is mounted on said sleeve 59 and is freeto slide vertically thereon. Rotatable on the slidable bearing block 60is a sheave 6I around which is wound a steel cable 62 to the endof whichis attached a driving weight 63. Below the sheave 6| and keyed totheshaft I1l is a clutch mechanism 64. The sheave 6| may be actuated intoand out of engagement with the clutch by means of a forked lever 65which engages the under surface of a keeper plate 66 for the raceway 60andsheave 6| which slides the sheave 6| and bearing block 6|)vertically, and which is pivoted on the base plate II at 66 and to whichis attached a rod 61 for automatic or hand operation. The operation oflever 66 lifts the sheave 6| off the clutch 64. The sheave 6| is fittedwith a stop 6Ia cooperating with a latch 6Ib for stopping the weight 63when in motion.

vThe blocks 24 and 25 are tted with handles 68 and 69 for swinging theblocks around the standard I2 on the hinges 26 and 21. The blocksmaintaining a constant temperature. Hot oil is also passed by gravitythrough the hollow shaft |1 from source 12 and allowed to drain outthrough drain 13, thus avoiding the friction that would be involved inoil tight connections. The oil passing through the shaft I1 maintainsthe cylinder I8 at a constant temperature and the cylinder I8 isprovidedwith a hole 14 for the insertion of a thermo-couple before andafter testing. Keyed to the upper end of the shaft I1 is a graduateddisc 15 which rotates with the shaft |1 under a fixed pointer 'I6attached to the top plate|4. A catch 11 is attached to the base plateand, as shown in Fig. 10, is adapted to hold the lever in a depressed orunclutched position.

Operation of laboratory type research plastometer A measurement of theabsolute viscosity of the material to be tested and the elastic recoveryof the same may be made inthe research plastometer as described below.With the pressure rings 43 and 44 in receding position as shown in Fig.1, and the blocks 24 and-25 swung into open position, as shown in dotand dash lines in Fig. I2, the sample to be tested is inserted Withinthe cylindrical surfaces 2|. 'I'he swinging blocks 24 and 25 are closedand clamped into position by means of the bolt 28 and nut 29. Guideplates 33 and 34 are swung out of the way, as shown in Fig. 5, and theexcess rubber above and below the reservoirs 4| and 42, which has beenpressed into the same by the closing of the blocks 24 and 25, is trimmedoi with a knife. The guide plates 33 and 34 are then placed in positionand locked. The pressure rings 43 and 44, faced with pads 45 and 46, areforced into position with the pads 45 and 46 exerting pressure on thematerial in the reservoirs 4| and 42 by means of the Weights |58 and 54.The material to be tested is-left in the chamber 23 two minutes topermit the material to attain the temperature of the instrument. Thedriving weight 63 operating through the steel cable 62, the sheave 6|,and the clutch l64, is then allowed to turn the rotor I8. This producesa shearing action on the rubber contained in the chamber 23 between thecorrugatons I9 on the rotor |8 and the corrugations 22 in the statorll.The beveled collars 31 and 38, as clearly shown in Figs. 3 and 4, arefree to rotate on the hollow shaft |1. The pressure pads 45 and 46acting on the material in the reservolrs 4I and 42 maintain a continuousand constat confining pressure on the material to be` tested .while itis being sheared by the rotation of the 'cylinder I0, thereby preventingslippage on the corrugations I9 and 22. The beveled collars 31 and 38serve to prevent the rubber in the reservoirs 4I and 42 from sticking tothe rotor and retarding this motion. After the cylinder I8 has beenrotated by means of the weight 63 and the weight has reached thefioor,the clutch 64 may be released, and the weight raised and made ready torotate the shaft again. The rate of rotation of the cylinder I8 may bemeasured with a stop' watch or other suitable means with the help of thegraduated disc 15 and fixed pointer .16. yWhen the sheave 6I is releasedfrom the clutch'f64, the elastic forces in the plastic material beingtested cause the rotor to jerk backwardsthrough a small angle and thento continue tti-creep slowly for some time. The extent of v4this reverserotation is a measure of the elastic recovery of the material and may bedetermined by'theqdisc 15 and the pointer 16.

Asstated above, in general terms, the instrument is characterized by theformula gtr-fluidity,

K 41I'LR22R12 in which R1=radius of rotor, R2=radius of stator,

L=length of rotor or stator.

The derivation of this formula, in slightly different notation, 'isgiven in Explicit formulas for slip and fluidity, M. IMooney, Journal ofRheology, vol. 2, p. 210 (1931) From this formula and measurements ofthe torque T applied to the rotor'and the angular velocity of rotationof the .shaft I1 or plate 15, under the torque T, the coefficient ofviscosity may be calculated. The elastic recovery, in absolute units, orangle of simple shear, may also be calculated from the following 2A inwhich a=angle of recovery, expressed in radians,

0=angular displacement of the rotor during recovery, expressed inradians.

Description of the plant type, experimental and control plastometerI-Referring now to Figures 6 to 8, wherein like reference charactersdesignate the same parts throughout the several views, |00 representsthe base plate of the instrument on the housing |0I.

To .the base plate |00 are attached standards |02 and |03 .on the upperends of which is mounted superstructure |04 in which eccentric |05v andcrank |06 operate to raise and lower connecting rod |01.

The upper end of the connecting rod |01 is attached to the crank |06 at|08 and the crank is pivoted on shaft |09 and made to operate throughhandle |I0. An adjustable screw III on' the top of standard |02 acts asa stop for the handle IIO of the crank in its downward movement whichlowers connecting rod |01. The pivot shaft |09 of the crank is alsomounted in circular eccentric |05 which rotates in a correspondingcircular bearing surface I|2 in the superstructure |04. 'Ihe eccentricmay be operated in the bearing surface I I2 through a. forked handle II4connected to the eccentric by the shaft |09 and the two pins II3. Thehandle ||4 carries an adjustable screw II5 which rests on handle ||0 ofthe crank |06 and limits the downward movement of the eccentric. Thehead of the screw |I5 also rests on the top of standard |03 whe/mtheeccentric is rotated to raise the connecting rod |01. In Fig. 6 theeccentric |05 and the crank I06'are shown in solid lines intheir/lowered position and the dot and dash lines wh/en the connectingrod |01 is in raised position. y

4The lower end -of the connecting rod I 01 is pivoted to the top plateII6 of the instrument by means of shaft II1. Raising and lowering of theconnecting rod |01 by means of eccentric |05 and crank |06 act to raiseand lower the top plate I6 which is guided in its movement by standards|02 and |03 passing through holes in thesame. Attached to the bottomsurface ||8 of the-top |00 is a shouldered collar |42 similar to theshoul-v truding from the top surface of the vforming with the upper |56in the depending portion |51 ofy base plate,

plate ls is a vsmnnderm collar is, which retains the plate |20 which iskeyed at |2| to the top plate, against the bottom surface ||8 by meansof screws "|22.l The lower margin |23 of the coll lar ||9 is corrugatedand forms with the bottom surface of the plate |20 the upper half ofjthe stator or outer wall of the chamber for containing the sample to betested. The lower surface |24 of the lplate |20 is roughened bycross-hatching, to leliminate slippage of the sample' to be tested, forexample, by cutting grooves at right angles to one another ,in thesurface.

The plate |20 contains two cylindrical chambers |25 in which are locatedplungers up by heavy springs |21 in holes |28 in the top plate ||6. Thesprings 21 are kept in engagement with the plungers nular collar |29attached to the top surface |80 of the top plate |6 by means of screws|3 The plungers 26 are formed with. ring tops v|32 proannular ring |29.The top plate l| I6 is provided with passages |33 for passage of a fluidmedium for temperature regulation constructed similarly to the passagesin the base platev |00 shown in detail in dotted lines in Fig. 8. Thetop plate is also provided with electric heating means. |34, and with agroove |35 on one sidefor reception of the stem of a thermometer |36.The thermometer is received in a hole which.is at right angles to thegroove |35 and extends to the center of the top plate ||6, correspondingto those in plate |00 shown in Fig. 8. The stem of the thermometer isbent at right' angles so as to lie in the groove.

The base plate |00, similar to the top plate |6, contains passages |31for the passage of a fluid 'medium for temperature regulation. Thepassages are shown in detail in dotted lines in Fig. 8 and the arrowsshow the path of ow of the fluid medium. The base plate |00 is alsoprovided with electric heating means |38 on the top surface |39 thereofand contains a groove |40 on one side thereof for reception of the stemof a kthermometer |4|, similar to the thermometer |36 in groove |35 intop plate ||6.

Attached to the top surface |39 of the base plate dered collar I9attached to the bottom surface of the top plate ||6. The collar |42retains the plate |43, which is keyed at |44, against the top surface|39 by means of screws |45. The upper margin |46 of the collar |42 iscorrugated, thus surface of the plate |43 the lower half of the statoror outer wall of the chamber for containing the sample to be tested. Theupper surface |41 of the plate |43 is roughened to eliminate slippageofthe sample to be tested by cutting grooves at right angles to oneanother in the surface. r

-A Co-axial with the stator and disposed within the chamber forcontaining the sample to be tested, is therotor |48. 'I'he top andbottom surfaces of the rotor are cut with grooves at right angles to oneanother similar to the surfaces |24 .1 and |41 of the platesv |20and|43. The periphery and also-by a lower shoulder |5| carried by the rotorfitting into a socket |52 in the plate |43. The shaft |53 for the rotor|48 is inserted into a 4 hollow spindle |54 and keyed to it by key |55.The

spindle |54 may be rotated in the vertical bearing |26 by means of ananmaterial to be tested is |00 by means presently to'be described.

Drive shaft |58 with gear teeth |59 cut in the end thereof which meshwith rotary gear |60 is driven by a synchronous motor not shown. Therotary gear f 60 is keyed to shaft |6| and is held fast to the shaftby-means of pin |62. i The shaft |6| is rotatable in horizontal bearings|63 and |64 in the housing |0|. The shaft |6| and gear |60 are movablehorizontally, the 'gear' |60 being in sliding mesh with the gear teeth|59 on drive shaft |58. A standard micrometer gage |65 is mounted inbracket |66 attached to the base plate |00 by screws |61, and thebearing pin |68 of the gage vis made to contact with one end |69 of theshaft |6|. The other end |68 of the shaft |6| contacts with the leafspring |69-held in mounting block |10 attached to the housing |0|. Aworm |1| is also keyed to the shaft |6| and is held in position on the.shaft by pin |12. The worm 1| meshes with a worm gear |13 which iskeyed to the vertical spindle |54 and held in position on it by means ofpin |14and lock plate |15.

Operation of the plant Atype experimental and control plastometer therotor is forced through a sheet or slab of the material to be tested,andthe rotor is then placed in the machine and pushed down intoengagement the a with the drive spindle |54. n this manner introducedbetween the bottomgrooved surface of the rotor and the top groovedsurface of the plate |43. Another piece of the material to be tested isthen placed on top of the rotor and the top plate |30 is forced into itslower position by means of levers connected to the eccentric |05 andcrank |06. As the edges ofthe shouldered collars ||9 and |42 approachone'another, the resistance to fiow of the excess 'which is beingsqueezed out of the testing chamberincreases, and some of the plasticmaterial, as the collars finally come into engagement with one another,is forced up into the reservoirs |25 against the plungers |26. Theseplungers are held against springs |21 and henceat all times maintain aconfining pressure on the material in the testing chamber so thatslippage of the material over the rotor |48 will produce a continuousshearing" action on the plastic material. After the material hasremained in the testing chamber for a minute or so and has come to thetemperature of the instrument, the synchronous motor attached tothe'drive shaft |58 is started and this in turn through the gears |59and'l60, and |1| and |13 produces a rotation of the rotor |48, therebyshearing'continuously the sample being tested. The resistance to thisshearing deformation of the sample tested develops a thrust in the'shaft|6| which presses against the leaf spring |69 and deflects it until theopposing force of the spring is equal to the thrust in theshaft. Thisdeflection is read on the gage |65 and is a measure of the shearingvforce, or the resistance of the material to the shearing action. Thegage reading usually passes through a maximum, sometimes followed by aminimum and finally, within one minute as a rule, becomes constant. Thisconstant reading is taken as the measure of the relative viscosity ofthe rubber. The high initial reading, followed by a lower reading, isdue principally to the thixotropy of the rubber or its tendency tosoften temporarily while being worked. A minimum in the gage reading,when it occurs, is due to air which has not yet been worked out of therubber; but as the air is gradually eliminated, the gage readingradually increases vto its proper value. The formula for the absoluteviscosity of material to be tested, as vabove stated, may be developedfrom the geometrical and other characteristics of the instrument as inthe laboratory type research plastometer; but it is preferable, as ageneral rule, to calibrate the plant type plastometer, when absolutemeasurements of viscosityA are desired, against samples standardized inthe laboratory 'type research plastometer. For practically allexperimental and control purposes, however, all that is desired is ameasurement of the relative viscosity of various materials, for whichthe plant type plastometer siiices With the'above detailed disclosuresof the invention, it is evident that numerous modifications will suggestthemselves to those skilled in the art, and it is not desired to limitthe invention otherwise than as set forth in the appended claims.

Having thus described my invention, what I claim and desire to protectby Lettersv Patent is:

1. A measuring instrument comprising means for subjecting a constantvolume of plastic material to a shearing action, means, acting directlyon the plastic material and maintaining it under confining pressure andconstant volume in the shearing zone while being so sheared, and meansfor indicating a resultant of the shearing force during said shearingaction. f

2. A measuring instrument comprising a rotor and a stator spaced fromeach other normally in iixed relation to provide a chamber of fixedvolume for test material, the material-engaging faces of said rotor andstator being roughened, andseparate means operating independently ofsaid rotor and stator for maintaining the chamber iull of material andunder continuous conning pressure, whereby slippage between the materialand the noughened surfaces is prevented when the material is sheared.

3. A measuring instrument comprising a stator and a rotor in ilxedrelative positions with clearance therebetween to provide a chamber offixed A volume for test material, the 'material-engaging surfaces ofsaid stator and rotor being roughened, and separate means operatingindependently of said rotor and stator for maintaining the materialunder continuous confining pressure, whereby slippage between thematerial and the roughened surfaces is prevented when the material issheared.

4. A measuring instrument comprising relatively movable parts defining ahollow stator, a rotor disposed within said stator whereby'upon theclosing of said relatively movable parts a substantially fixed volume ofmaterial is confined about the rotor, the material-engaging surfaces ofsaid stator and rotor being roughened, and means operating indendentlyof the rotor for applying a continuous compressive force to thematerial, whereby slippage is prevented betweenl the roughened surfacesand the conflned. material when the material is sheared.

5. In a testing machine, a rotor, a plurality of CII municating withsaid chamber, and pressure means acting upon the material in saidreservoir for maintaining the material in the reservoir and chamberunder continuous confining pressure without interfering with theshearing action of the rotor upon the material within the chamber.

7. In a testing instrument, a stator, a rotor in iixed spaced relationto said stator for deiining a chamber of fixed volume for material undertest, a reservoir outside of the zone of shearing action between therotor and stator and communicating with said chamber, and means actingupon the material in said reservoir for maintaining the material in saidreservoir and chamber under continuous confining pressure. l

8. A measuring instrument comprising a rotor with a roughened surface, astator with a roughened surface and composed of movable sections, meansfor forcing the movable sections of the stator into fixed positionsrelative to the rotor so as to cut and form a sample of test materialabout the rotor, separate means for applying continuous conning pressureto the sample without altering the relative position of stator androtor, and means for measuring the resistance of the sample to relativemovement between the stator and the rotor.

9. A measuring instrument comprising a rotor with a roughened surface, astator with a roughvened surface and composed of movable sections,

` about the rotor, and separate means for applying continuous coniiningpressure to the sample withoutaltering the relative position of statorand rotor.

10. A measuring instrument comprising a' stator and a rotor in xedrelative positions with clearance therebetween to provide a chamber ofxed volume for test material, the materialengaging surfaces 'of saidstator and rotor being roughened, separate means operating independentlyof said rotor and stator for maintaining the material under continuousconning pressure whereby slippage between the material and the roughenedsurfaces is prevented when the material is sheared, and measuring meansassociated with the rotor. y

11. In a measuring instrument, a stator, a rotor in xed spaced 'relationto said stator to provide a chamber of fixed volume for test material, areservoir communicating with said chamber, pressure means acting uponthe material in said reservoir for maintaining the material in thereservoir and chamber under continuous conlining pressure withoutinterfering with the shearingaction of the rotor upon the materialwithin the chamber, and means for measuring a force responsive to theshearing action in the material.

MELVIN MOONEY.

